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Short and sweet. Just one thing to add:
I (unwillingly) left my comfort zone when I tried to solve the first exercise in “Mastering Chess Middlegames: Lectures from the All-Russian School of Grandmasters” by Alexander Panchenko. Going through the first chapter on the attack was very interesting and I had no problems following the illustrative examples. But then came the first exercise. After 20 minutes I still felt that I did not got it right and checking the solution confirmed that.
But what I want to add is that with dealing with problems out of your comfort zone not only comes growth.
Typically you will see new ideas or more sides of the beauty of chess. Seeing and understanding the solution of the exercise was really an aesthetic/mental enjoyment and a great reward for leaving the comfort zone.